The Rev peptides that bind to the Rev-Response element are 25 residues long, and form a weak alpha helix. Of the 25 residues, there are 12 arginines, making assignment of the peptide resonances extremely difficult. In addition, the structure of the N-terminus of the peptide appears to be critical for recognition. We are examining larger fragments of Rev containing the RNA-binding domain and additional sequences toward the N-terminus. The Rev(1-50) sequence forms a compact structure in the presence of 7% trifluorethanol, and we are characterizing this structure using 15N-labeled peptide produced by overexpression. In addition, this larger protein fragment forms a specific complex with the RRE RNA. Although the spectra are of lower quality than with shorter peptides, we should be able to confirm the structure of the critical N-terminal region of the RNA-binding domain.